C. David Sherrill of the Georgia Institute of Technology is supported by the Theoretical and Computational Chemistry Program to develop and implement new methods to treat electron correlation more efficiently. He is constructing a hybrid method that computes the most important double excitations with coupled-cluster (CC) theory, and less important methods using second-order Moller-Plesset perturbation theory (MP2). The most important triple excitations are selected using a combination of active-space and macroconfiguration concepts. Planned applications include studies of the lattice energy of crystal benzene, potential energy surfaces for species with pi-pi interactions, substituent effects on the binding energies of intercalators to nucleic acid base pairs, barrier heights for hydrogen transfer reactions, and near degeneracies in Mn-based catalysts. This work is having a broad impact in that the PSI3 package developed by the PI and his group is freely available and open source. The proposed applications to study pi-pi interactions are important in such areas as drug-target interactions. An experimental collaboration is improving the education of a broader group in high-level electronic structure methods. The results of this research are incorporated into web notes and summer workshops taught by the PI.
